A classical system in which electrical charge can be transferred or shuttled mechanically uses two large capacitor plates and a metalized ball (or particle) suspended between the plates. Charging one of the plates (and grounding the other) will attract the ball to the charged electrode via the Coulomb force and upon contact with the plate the ball will exchange electrons with the plate. The acquired excess charge in the ball will in turn accelerate the ball in the electric field between the plates to the grounded electrode, where the excess electrons are dumped upon contact. Depending on the system geometry (plate and ball size and distance between the plates), applied voltage, and the manner in which the ball is suspended, the ball will cycle back and forth between the plates at a frequency which may reach a few kHz. The result is an effective transfer of charge (i.e., a current flow) between the plates.
The integration of a mechanical degree of freedom in nanostructures utilized in nanoelectromechanical systems (NEMS) opens a potential wide range of applications in, for example, sensors and communication electronics. Mechanical resonators manufactured with nanometer dimensions have been formed to oscillate at radio frequencies up to the range of GHz. See, e.g., R. H. Blick, et al., J. Phys.: Cond. Mat. 14 (2002) R905; X. M. H. Huang, et al., Nature (London) 421 (2003) 496. Significant progress has been made with regard to the control of non-linear dynamics and dissipation of NEMS at radiofrequencies. D. V. Scheible, et al., Appl. Phys. Lett. 81 (2002) 1884; D. V. Scheible, et al., Appl. Phys. Lett. 82 (2003) 3333; F. W. Beil, et al., Phys. Rev. Lett. (2004) (submitted for publication). NEMS also have promise for providing experimental insight into the quantum aspects of mechanical systems.
Efforts have been made to implement a mechanical charge shuttle into NEMS structures by combining a nanomechanical resonator with a single-electron transistor (SET). Such nanomechanical charge shuttles were formed by combining cantilevers with SETs fabricated on the tips of the cantilevers to form a so-called electromechanical SET (or EMSET). A. Erbe, et al., Appl. Phys. Lett. 73 (1998) 3751; A. Erbe, et al., Phys. Rev. Lett. 87 (2001) 096106. These devices were achieved using traditional NEMS fabrication utilizing optical and electron beam lithography of layered silicon substrates incorporating a sacrificial layer. Experiments with these devices showed electron tunneling that was mechanically chopped at radio frequencies. It would be desirable to be able to increase the operating frequency preferably to several hundred MHz and into the GHz range, and to be able to fabricate charge transfer devices utilizing semiconductor processing techniques that are more compatible with standard integrated circuit manufacturing.